Question

During a thunderstorm, rain water contains nitric acid. Why?

Answer 1

1. This process involves three chemical reactions:
   (i) Atmospheric nitrogen reacts with atmospheric oxygen to form nitric oxide due to lightning discharge.
   ${\mathrm{N}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{NO}\left(\mathrm{g}\right)$
2. ii) The nitric oxide is further oxidised to nitrogen dioxide.
   $2\mathrm{NO}\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)⟶2{\mathrm{NO}}_2\left(\mathrm{g}\right)$
3. iii) The nitrogen dioxide dissolves in atmospheric moisture in the presence of oxygen and forms nitric acid which comes along with rain.
   $4{\mathrm{NO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 4{\mathrm{HNO}}_3\left(\mathrm{l}\right)$
4. As a result, during a thunderstorm, rain water contains nitric acid.